Adhering textiles and metals to rubber and product

ABSTRACT

BONDING OF RUBBER TO TEXTILES OR METALS UTILIZING A VULCANIZABLE RUBBER CONTAINING A FORMALDEHYDE DONOR, A FORMALDEHYDE ACCEPTOR AND A FINELY DISPERSED SILICA FILLER.

United States Patent ()flice 3,751,331 Patented Aug. 7, 1973 3,751,331 ADHERING TEXTILES AND METALS TO RUBBER AND PRODUCT Ivo Dane, Leverkusen, Guido Fromandi, Schildgen, Paul Blankenstein, Cologne-Rich], Erwin Muller, Leverkusen, Helmut Freytag, Cologne-Stammheim, and Wolfgang Huther, Cologne-Mulheim, Germany, assignors to Bayer Aktiengesellschaft, Leverkusen, Germany No Drawing. Original application Sept. 19, 1966, Ser. No. 580,205, now abandoned. Divided and this application May 25, 1970, Ser. No. 40,370 Claims priority, application Germany, Oct. 2, 1965, F 47,344 Int. Cl. B32b 5/02, 5/16, 15/06 US. Cl. 161-83 13 Claims ABSTRACT OF THE DISCLOSURE Bonding of rubber to textiles or metals utilizing a vulcanizable rubber containing a formaldehyde donor, a formaldehyde acceptor and a finely dispersed silica filler.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 580,205 as filed Sept. 19, 1966 and now abandoned.

Textiles are incorporated into numerous products of the rubbery industry, such as motor car tires, conveyor belts, driving belts, V-belts, hoses, shoes, etc., usually for the purpose of reinforcement. One important requirement in all these cases is that a good bond should be obtained between the rubber and textile, but this is not achieved without special measures being taken, especially when semi-synthetic or fully synthetic fibres are used.

In order to obtain sufiicient bond strength with the rubber, the textiles usually have to be pre-impregnated. Such pro-treatments are nowadays generally carried out using natural and synthetic rubber latices with the addition of resorcinol formaldehyde resins dissolved or dispersed in water, which resins are normally not completely condensed and undergo further condensation by the addition of formaldehyde in the course of the subsequent working process. In many cases, however, the bond strength obtained by such impregnation is not sufficient.

In recent years, processes for further improvement of bond strength have become known in which certain compounds, of which a number will be mentioned hereinafter under the examples of compounds which give off formaldehyde, are added in combination with resorcinol or certain other resorcinol derivatives mentioned below to the textile which has either been pre-impregnated or not undergone preliminary treatment.

It has now been found that a very substantial increase in the bond strength between rubber and textiles can be achieved if in addition to compounds which are capable of splitting off formaldehyde on heating, in some cases in the presence of water, and in addition to m-disubstit-uted benzene derivatives which are substituted by amino groups or by hydroxyl groups which may be etherified or esterified or condensates thereof with dialkyl ketones or formaldehyde or alkyl or aryl aldehydes or 1,5-dihydroxynaphthalene (this latter instead of the benzene derivatives), finely dispersed silica fillers are also added to the vulcanisable rubber mixture which is to be applied to the textile and is subsequently vulcanized. Instead of the benzene derivatives mentioned above, one could also use precondensed but not yet completely condensed resorcinol formaldehyde resins. The improvement in bond strength occurs not only in textiles which have undergone pretreatment for improving the bond but also to a particularly marked extent in textiles that have not been pretreated. The bond strength that can be achieved by the addition of silica filler and the above-mentioned benzene derivatives is, of course, not equally high in the case of all products that split off formaldehyde, but in the case of some splitters, the improvement in the bond strength is so great that in many cases the bond strengths obtained on textiles that have not been pretreated are of a value that has hitherto only been obtainable, in the prior art, by pretreatment of the textiles. The special pretreatment of textiles, which have hitherto been unavoidable, may therefore be unnecessary for many fields of application by reason of the process according to the invention.

By formaldehyde-splitting compounds are to be understood those compounds which are capable of splitting olf formaldehyde when heated, e.g. to temperatures in the region of 40 to 200 C., in particular under vulcanisation conditions, optionally in the presence of water. When methylolethers or methylolesters are used, condensation reactions may also occur which split off alcohols or acids. Such products will hereinafter briefly be termed formaldehyde splitters.

The following are examples of formaldehyde splitters:

trimetric methyleneamino-acetonitrile,

'1-aza-3,7-dioxabicyclo-[3,3,01-octane or oxazolidines,

bis- 1,3-oxazolidine) methane, octahydro- 1 ,3-benzoxazole,

tetrahydro-1,3-oxazine, dialkylamino-methylalkyl-ether,

diallylamino-methyllalkylether (see e.g. Belgian patent specification 621,923),

for example 4,4-dimethyl-1,3-oxazolidine, bis-(4,4-dimethyl-1,3-oxazolidine)-methane, N,nbutyl-5 (6) -cyano-octahydro-1,3-benzoxazole, 3-n-butyl-tetrahydro-1,3-oxazine, diisopropyl-aminomethyl-ethyl ether, diallyl-a-minomethylethyl-ether, hexa(methoxymethyl)melamine, N-methylol-carboxylic acid amides,

such as, for example,

N-methylolacetarnide, N-methylol-butyramide, N-methylol-acrylamide, N-methylol-methacrylamide, N-methylol-succinimide and N-methylolmaleic acid imide.

The following are examples of further formaldehyde splitters: 1,8-di-(methyleneamino)-p-methane or azomethine, for example a,a-dimethyl-benzylazomethine (see US. patent specification 2,512,128), or cyclotrimethylenetriamines such as N,N,N"-trimethyl-cyclotrimethylenetriamine or N,N,N" triethyl-cyclotrimethylenetriamine, diaminomethanes disubstituted on both N-atoms, e.g. bis[di(cyanomethyl)amino]-methane or bis(diallylamino)methane, imidazolidines substituted on both N-atoms, e.g. N,N'- diphenyl-imidazolidine or N,N'-dibenzylimidazolidine or hexahydropyrimidines substituted on both N-atoms, e.g. N,N'-di-n-hexyl-hexahydropyrimidine (see Belgian patent specification 624,519). Hexamethylenetetramine is an example of another heterocyclic compound.

Other formaldehyde splitters that can be used according to the invention are methylol melamines such as hexamethylol melamine some or all hydroxyl groups of which may be etherified or esterified. The hexamethylolmelamine used need not be present in pure form but may be used in the form of products which have a slightly lower formaldehyde content or which contain higher molecular weight condensation products. Hexamethylolmelamine may be prepared in known manner, e.g. by reacting about 1 mol of melamine with about 6 mols of aqueous formaldehyde solution see Helvetica chimica aeta, 24, p.

3 315 E; Swiss Pat. 197,486; and Houben-Weyl Methoden der organischen Chemie, vol. 8, p. 242).

As already mentioned above, instead of hexamethylol melamine one may use its esters or ethers, which may be regarded as masked methylol compounds. Compounds which are suitable in the present case as well as in the cases given below of the use of ethers or esters are in particular lower alkyl others such as, for example, methyl-, ethyl-, propyl-, butyl-, and allyl ethers, in which case 1 to 6 hydroxyl groups may be etherified Especially suitable esters are lower aliphatic carboxylic acid esters such as acetates and propionates. Examples of such compounds are hexamethylol melamine acetate and hexamethylol melamine propionate. Furthermore, one may, of course, also use, methylol melamines which contain at the most 5, and preferably 3 to 5, methylol groups per mol, which methylol groups may be all or partly etherified or esterified. The compounds are prepared by methods known per se by reacting melamine with the desired quantity of formaldehyde and, if desired, etherifying or esterifying the resulting methylol compounds (see Houben-Weyl Methoden der organischen Chemie, vol. 8, p. 358). In general, this process does not lead to chemically uniform compounds but to mixtures of different types of methylol compounds which may also be used. The same applies to esters and ethers as has been said above of hexamethylolmelamine. Examples of such compounds are: pentamethylol melamine acetate and pentamethylol melamine propionate.

Tetramethylol-hydrazo-dicarboxylic acid amide the hydroxyl groups of which may also be either all or partly etherified or esterified may also be used. It is particularly advantageous to use the crystalline form of tetramethylol-hydrazo-dicarbonamide which is obtained by reacting hydrazo dicarbonamide with 4 mols of formaldehyde (see Houben-Weyl, Methoden der organischen Chemie, vol. 14/2, p. 352). Instead of the pure compound (M.P. 149 C.), resinous condensation products containing more or less formaldehyde may also be used. Examples of esters and ethers are tetramethylol-hydrazo-dicarbonamide-acetate and -propionate.

In addition, the following compounds may be used as formaldehyde splitters: Tetramethylol-acetylene-diurea, the hydroxyl groups of which may also be all or partially etherified or esterified. Tetramethylol-acetylene-diurea need not be present in the pure form but may be used in the form of products which have a slightly lower formaldehyde content or which contain higher molecular weight condensation products. The preparation of tetramethylol-acetylene-cliurea may be carried out in known manner, e.g. according to Houben-Weyl Makromolekulare Chemie" 2, p. 353. The following are examples of esters and ethers: Tetramethylol-acetylene-diurea-tetramethyl ether and tetramethylol-acetylene-diurea-tetraacetate.

Formaldehyde splitting methylol compounds, in particular N-methylol compounds and their derivatives in which the hydroxyl groups may also be entirely or partly etherified or esterified, e.g.

N,N'-dimethylolurea, dimethylol-urea-dimethylether, N,N'-dimethylol-uronic-dimethyl ether, methylene-bis-(methylol-urea-methyl ether), dimethylol-urea-di-n-butyl ether.

N-substituted 1,3,5-dioxazines which may be substituted by straight or branched, saturated, or unsaturated alkyl, cycloalkyl, aryl or aralkyl radicals, which radicals may in turn be substituted and in which the substituent (on the nitrogen atom) may also contain further dioxazine rings. Examples of such compounds are: N-allyl-1,3,5-dioxazine; Nn-butyl-l,3,5-dioxazine; N-isobutyl-l,3,5-dioxaziue; N- cyclohexyl-1,3,5-dioxazine; N-phenyl-1,3,5-dioxazine; N- (B-hydroxyethyl)-1,3,5-dioxazine; N ethyl-acetate-1,3,5 dioxazine; or N,N '-e thylene -bi s-(1,3,5-dioxazine).

The dioxazines may, for example, be prepared in known manner by reacting the corresponding amines with an excess of formaldehyde. Instead of the pure compounds, one may also use the mixtures obtained by such a preparation with condensation products which contain a varying quantity of formaldehyde. Paraformaldehyde may also be used.

Particularly high bond strengths have been obtained with rubber mixtures treated with the silica fillers according to the invention in cases where the following compounds were added in combination with resorcinol:

hexamethylol melamine;

hexamethylol melamine-pentamenthylether;

a mixture of hexamethylol melamine tetramethylether and -trimethylether;

pentamethylol melamine-trimethylether;

tetramethylol hydrazo-dicarbonamide;

tetramethylol-acetylene -diurea;

N,N'-dimethylol-urea;

N-methylol-dicyandiamide;

methylene-amino-acetonitrile;

N-allyl-dioxazine,

N-phenyl-dioxazine and 1-aza-3,7-dioxa-bis-cyclo-[3,3,0]-octane.

As already mentioned above, the formaldehyde splitters are used together with resorcinol or other benzene derivatives which are preferably substituted in the m-position by amino groups or by hydroxyl groups which may be etherified or esterified or its condensates with dialkyl ketones or formaldehyde or alkylor aryl aldehydes or 1,5- dihydroxy-naphthalene. Examples of such derivatives are as follows: m-Aminophenol; m-phenylendiamine; resorcinol diacetate or propionate or butyrate, resorcinol monomethyl ether or resorcinol propyl ether.

Resorcinol formaldehyde resins which have been precondensed but not completely condensed may also be used as additives to the mixture.

When the resorcinol which is particularly effective is used, it has been found advantageous in the working up process to use a type of formaldehyde splitter in which resorcinol is soluble since solutions of resorcinol in formaldehyde splitters can be added after the rubber mixtures have cooled to below 100 C., if desired together with sulphur or the vulcanisation accelerators. The temperature conventionally used for incorporating resorcinol at which dense clouds of noxious vapour are emitted which can cause great discomfort to the operators is thus avoided. The nuisance caused by the resorcinol vapours can also be avoided in a similar manner by dissolving resorcinol in suitable plasticizers and then adding it as described above at the end of the mixing process.

For the exceptional increase in bond strength obtained according to the invention the use of finely dispersed reinforcing silica fillers in the rubber mixture is of essential importance. By finely dispersed reinforcing silica fillers is to be understood substances having a silica content of more than by weight based on dry filler and a specific surface, determined by nitrogen absorption according to BET (S. Brunauer, P. H. Emmet, E. Teller, Journal of the American Chemical Society 60, 309 [1938], of about 70 to 400 m. /g., preferably 80 to about 200 mF/g. corresponding to an average primary particle size of about I 0.007 to 0.04/L, preferably an average primary particle size of about 0.013 to about 0.035 Such silica fillers may be prepared e.g. by precipitation from silicate solutions or by hydrolysis of silicon halides in the gaseous phase or by volatilisation via silicon monoxide as intermediate stage, at high temperatures. It is preferred to use silica fillers which have been prepared by precipitation for the process according to the invention. The silica fillers may contain silicates such as calcium and/or aluminium silicates.

It has been found that an increase in the stearic acid content above the usual level, ie stearic acid contents of 1 to by weight, preferably 2 to 3% by weight based on the rubber, in many cases still further increases the bond strength in the rubber mixtures according to the invention.

A really firm bonding effect is achieved in the rubber mixture to be applied to textiles if the amount of active silica filler added is at least 15% by weight. If the amount of additive is smaller, the bond strength decreases; where larger amounts of additive are used, the bond strength can be increased still further by a considerable amount. Above 70 to 100% by weight, increase in bond strength is generally only slight (percentages based on rubber). The formaldehyde yielding compounds are advantageously added in amount of between 0.2 and by weight, preferably between 0.5 and 5% by weight. The improvement in bond strength is considerably enhanced by adding quantities of resorcinol or other N-substituted benzene derivatives which are approximately equal to the amount of the formaldehyde splitter, preferably between 0.2 to 2 times the quantity. During the operation of mixing resorcinol into the mixture, the temperature should lie above the melting point of resorcinol (about approximately 115 Q). Where the other benzene derivatives mentioned above are used, it is also advantageous if they are added when the temperature of the rubber mixture is above their melting point.

The types of rubber that may be used include both natural and synthetic rubber such as copolymers of butadiene styrene, butadiene-acrylonitrile, isobutylene-isoprene, ethylene-propylene (usually with a third component such as dicyclopentadiene or 1,4-hexadiene), and in addition, polyisoprene, polybutadiene, polychlorobutadiene etc. as well as mixtures thereof.

Suitable textile materials are threads (in particular cords), as well as woven and knitted fabrics from all types of fibres such as rayon, polyamide, polyester, polyacrylonitrile, cotton, glass and other fibres. Thick wires of polyamide or polyester as well as cord threads from raw steel and zincor brass-coated steel may also be used. If bond improving pre-impregnation of the textiles is desired, this can be effected by use of the usual impregnating baths used in the art which contain, for example, latices based on natural rubber or copolymers of butadiene-styrene, butadiene-acrylonitrile, chlorobutadiene or butadienestyrene-vinylpyridine or mixtures thereof and, preferably, resorcinol formaldehyde resins.

The rubber mixtures according to the invention are applied to the textiles by processes usual in the rubber industry. The rubber mixtures are preferably put into the process in solid form but one may also use solutions of the mixtures in organic solvents. e.g. by painting, impregnating or spraying them as adhesifying intermediate layer to the fabric. In contrast to other processes of this type used in the art, e.g. in the case of solutions of rubber mixtures with isocyanate additives, the solutions of the mixtures according to the invention afford the technically important advantage of being storable for prolonged periods. After the bond-imparting pretreatment, subsequent coating of the textiles with mixtures free from additives can be carried out by painting or backing.

The three components of the mixture according to the invention, resorcinol, formaldehyde splitters and silica reinforcing fillers, need not all be present in the rubber mixture from the start. It is also possible first to apply one or two of the said components, e.g. resorcinol or resorcinol and/or formaldehyde splitters in the form of a solution into the textile and then add only the remaining component(s) to the rubber mixture so that the required 3 components only come together during vulcanisation. One may use organic solvents alone but also a concentrated solution in an organic solvent may be emulsified in water with the use of a suitable emulsifier so that the operation of applying the additive to the textile takes place largely in an aqueous medium, which 6 is commercially preferable. This process also makes it possible to avoid the formation of heavy smoke clouds of resorcinol at high temperatures.

It has been found that the combination according to the invention of formaldehyde splitters, resorcinol or'the said resorcinol derivatives or precondensed resorcinolformaldehyde resins and finely dispersed silica fillers also gives a substantial improvement in the adhesion of textiles to latices of the said types of rubber. In that case, the two first mentioned components are introduced into the latex mixture as solutions or aqueous dispersions. The finely dispersed silica is added in the form of aqueous silica sols in which the primary particles of silica are within the range mentioned for the primary particles of the fillers.

Vulcanisation of the finished article may be carried out in the customary manner. Provided the mixture is of the appropriate composition, it is however also possible to use very brief heating times at very high temperatures, e.g. about 1 to 2 minutes at 180 C. or about 0.5 to 1 minute at 200 C.

The following silica fillers are used in the examples given below:

SILICA FILLER 1 Commercial silica prepared by precipitation from silicate solution, having a specific surface area of 180 m.'/ g. (e.g. trade product Vulkasil S of Farbenfabriken Bayer AG., Leverkusen).

SILICA FILLER 2 Commercial silica containing calcium silicate and pre- .pared by precipitation from silicate solution and having a specific surface area of mP/g. (e.g. trade product Vulkasil C of Farbenfabriken Bayer AG., Leverkusen).

SILICA FILLER 3 v Commercial silica obtained by hydrolysis in the gaseous phase, having a specific surface of 200 mP/g.

Example 1 The following rubber mixtures were prepared on mixing mills:

Parts by weight #NDIOI 000 00cc wP-NUU 000. 0

Aromatic mineral oil.. Styrenated diphenylarmne Benzthiazyl-Z-eyclohexylsulphenamide r Condensation product of acrolein with aromatic bases co oomaooo phur Hexamethylolmelaminepentamethyl ether In the case of mixtures 1b and 1d, preliminary mixtures of rubber, carbon black, silica filler and resorcinol were first prepared at a mixing temperature of 130 C. When these preliminary mixtures had cooled down to about C., the remaining components of the mixture and lastly hexamethylolmelamine-pentamethylether were added. Mixtures la and 1c were prepared in the same way but without the addition of hexamethylolmelamine pentamethyl ether.

Sheets of about 1 mm. thickness made from these mixtures were placed each between two sections of nonpretreated cross-woven fabrics: cotton warp threads Nm 20/2 per 10 cm., 105 weft threads Nm. 20/2 per 10 cm., weight per square metre 240 g.); rayon (240 warp threads TD 450/ 1 per 10 cm., weft th'reads TD 900/1 per 10 cm., weight per square metre 320 g.); nylon (250 7 warp threads TD 810/1 per 10 cm., 120 weft threads TD 810 per 10 cm., weight per square metre 440 g.); and polyester (I170 weft threads TD 900/1 per 10 cm., 130 warp threads TD 1000/1 per 10 cm., weight per square metre 370 g.). These sheets were then vulcanised in a press under a pressure of 20 kg./cm. 2.5 cm. wide strips were stamped out of the plates produced in this way. The force required for separating one of the strips of fabric from ruber was treated on a stress-strain testing machine in which the force was indicated without inertia, at room temperature. The test results were evaluated with the aid of the stress-strain diagram, the means value being determined from the 10 highest value of a diagram in each case. Each of the test figures given below was obtained from 5 test strips. The following results were determined:

Bond strength in kg. per 2.5 cm.

Mixture 1a lb 10 1d Fabric:

Cotton fabric 2. 7 4. 6 3. 8 8. 6 Rayon fabric--. 1.5 2. 5 3. 2 15.8 Nylon tabrlcm- 1.1 3. 3 2. 4 17. 5 Polyester fabric 1. 2. 3 2. 4 5. 6

Example 2 Tests analogous to those in Example 1 were carried out with the same untreated fabrics but with modified mixtures 2a to 2e. The part of the mixtures which remains the same is termed hereinafter the basic mixture I.

It has the following composition:

BASIC MIXTURE I Condensation product of acrolein and aromatic bases 1.0 Sulphur 2.0

The other substances added to basic mixture I are summarised below:

Additions to batsis mixture I in parts Mixture 2a 2b 2c 2d 2e Nature of additives:

MT black 35.0 10. 0 10. 0 10. 0 10. 0 Silica filler 2 40. 0 40. 0 Silica filler 3. 30. 0 30.0 Resorcinol 2. 2. 5 Hemamethylolmelanune 2. 0 Hemamethylolmelaminepcntamethyl ether 2. 5

The following results were obtained in bond strength tests corresponding to Example 1:

Bond strengths in kg. per 2.5 cm.

Mixture 2a 2b 2c 2d 2e Fabric:

Cotton tabn'c. 2. 7 3. 5 11.3 2.6 6.1 Rayon fabric. 1. 5 1. 5 13. 4 0.5 15. 2 .Nylon iabrim 1. 1 1. 2 26. 7 2. 5 14. 4 Polyester fabric 1. 0 1. 2 9. 0 0. 4 4. 8

Example 3 In a manner analogous to Example 2, bond strength tests were made with use of the same untreated fabrics and the m x u e 3a o 3c i di at d elow. he substances added to the basic mixture I defined in Example 2 being again listed.

Additives to basic mixture I in parts by weight Mixture 3a 3b 30 Nature of additives:

MT black 35.0 35.0 10.0

Silica filler I 30.0

Resorcinol 2.5 2.5

Tetrarnethylolhydrazone-dicarbonamid 2. 0 2. 0

The following bond strengths were found:

Bond strengths in kg. per 2.5 cm.

Mixture 3a 3b 30 Fabric:

Cotton fabric 2. 7 7.0 12. 9

Rayon fabric. 1. 5 4. 8 17.5

Nylon fabric 1. 1 9. 5 24. 7

Polyester iabri 1. 0 2. O 8.0

Example 4 The following mixtures were prepared and tested in a manner analogous to Example 2:

Additives to basic mixture 1 in parts by weight Mixture 4a 4b 4c 4d Nature of additives:

T black 10. 0 10. 0

Silica filler 1. 30.0 30.0

Resorcinol 1. 3 1.3 2. 6

Lazar-3,7-dioxabicyclo[3,3,0]octan 1. 0 1. 0 2. 0

The following bond strength values were found:

Mixture 4a 4b 4c 4d Fabiic:

Rayon fabric 1. 5 2. 2 6. 5 7. 3 Nylon fabric 1.1 3. 4 7. 4 11. 3

Example 5 The following mixtures were prepared and tested in a manner analogous to Example 2:

Additives to basic mifiture I in parts by weig Mixture 5a 5b 5c 5d 5e Nature of additives:

MT black 35. 0 35. 0 10. 0 35. 0 10. 0 Silica filler 1 30. 0 30. 0 Resorcinol. 2. 5 2. 5 2. 5 N -allyl-1,3,5-dioxaz1ne 2. 0 2 0 N-phenyl-l,3,5 dioxazine 2. 0 2. 0

The results were as follows:

Bond strengths in kg. per 2.5 cm.

Mixture 5a 5b 5c 5d 5o Fabric:

Nylon fabric 1.1 6. 5 12.1 9. 7 11.5

Example 6 Bond strength tests were carried 'out with glass fabrics (225 warp threads TD 580 per 10 cm., weft threads TD 580 per 10 cm., weight per square metre 280 g.) in a manner analogous to Example 2. Mixtures 1a, 1b, 1c, 1d and 2c were used. The following results were obtained:

Bond strengths in kg. per 2.5 cm.

1b 1c 1d Mixture Glass fabric 9 Example 7 In a manner analogous to Example 1, tests were carried out with the following mixtures based on butadieneacrylonitrile rubber:

Components of mixture in parts by weight Mixture 7a 7b 7c 7d 70 Nature of components:

Butadiene-acrylonitrile rubber SRF black FEF black Silica filler 1 Resorcinol.. Zinc oxide Coumarone resin Xylene-formaldehyde res Stearic acid N -phenyl-N-cyclohexylp-phenylene diarnine Phenyl-a-nuphthylamine Sulphur N-diethyl-Z-benzthiazylsulphenamide Hexamethylolmelamine pentamethylether In the same way as in Example 1, preliminary mixtures of rubber, carbon black, silica fillers and resorcinol were first prepared at about 130 C. The remaining constituents were added after the mixture had cooled to about 100 C. (see Example 1).

The subsequent test procedure was again the same as in This example is intended to show that the additives according to the invention also increases the bond strengths in textiles which have already been impregnated to improve the bond strength. The test was carried out on a polyester cord (TD 800/1 x 2) pretreated on the basis of a solution of a rubber mixture with isocyanate additive and on nylon cord (TD 1680/1 x 2) pretreated on the basis of latex and resorcinol formaldehyde resin.

The rubber mixture 8a used for pretreating the polyester cord had the following composition:

Mixture 8b Parts by weight Natural rubber 100.0 Zinc oxide 20.0 HAF black 40.0 Coumarone resin 4.0 Aromatic mineral oil 3.0

After this mixture 8a had been dissolved in benzene in the ratio of 1:5 then parts by weight of tripentylmethane triisocyanate, based on the dry rubber mixture, were added. The polyester cord was impregnated with this solution.

The nylon cord was treated with an impregnating mixture of the following composition:

Parts by weight Latex of a copolymer of butadiene, styrene and vinyl pyridine, 40% 250.0 Precondensed resorcinol formaldehyde resin 20.0 Formaldehyde solution, 30% 20.0 Water 340.0

630.0 Total dry content 20% These nylon cords were heated for about 10 minutes at 135 C. in the course of the drying process.

Mixtures 1a, 1b, 1c, and 1d were used for incorporation by vulcanisation into the pretreated polyester and nylon cord.

The cords were embedded in each case between two strips 40 cm. in length, 3 mm. in thickness and 2 cm. in width prepared from these mixtures, the cords being embedded perpendicularly to the direction of the strips and at intervals of 1.5 cm. Vulcanisation of the test samples containing the cords was carried out for 50 minutes at 138 C.

To determine the static bond strength, individual test samples 1.5 cm. in length were punched out of the test strips in such a way that each sample contained one cord (embedded to a length of 2 cm.) in the middle. After preheating to C., the force required for pulling the cord out of the rubber was measured in a chamber heated to 80 C.

The test method is fully described in Bayer-*Mitteilungen fiir die Gummi-Industrie N0. 29, pages 71 to 78.

' The following bond strengths were obtained:

Static bond strengths (kg) at 8 Mixtures 1a, 1b and 1d were dissolved in benzene in the ratio of 124.5 and then applied in a thickness of about 0.5 mm. to the rayon fabric described in Example 1 by several applications by means of a spread coating machine. After drying, the sections of fabric were .folded double and then vulcanised partly in a press under-a compression pressure of 20 kg./crn. partly in superheated steam at 2.5 atmospheres above atmospheric pressure and partly in hot air at 138 C. (=25 atmospheres above atmospheric pressure) with an additional air pressure of 3 atmospheres above atmospheric pressure.

Strips 2.5 cm. in width were punched out of the vulcanised sheets and then investigated by tests analogous to those in Example 1. The results were as follows:

The effect of the additives according to the invention in tyre mixtures of pure natural rubber on the bond strength of non-impregnated and impregnated rayon cord is investigated. The rubber mixtures used had the following composition:

Parts by weight Mixture 10a 10b 10c 10d Natural rubber 100. 0 100. 0 100. 0 100. 0 Zinc oxide 2.0 2. O 2. 0 2. 0 SRF black 25. 0 25. 0 Silica filler 1 25 25. 0 Resorcinoh. 2. 5 2. 5

P rt i ht 126 warp threads of polyester yarn TD 1000/3 per 10 a shy we g cm., 46 weft threads of nylon yarn TD 840/3 per 10 cm., Mixture 10a 10b weight per square metre 600 g. Steam acid" 0, 5 The following values for bond strength were obtamed: Pine tar 3.0 3.0 8.0 3.0 5 tt fifffiii iiiii fiff: 5:2 5:2 $13 t3 Bondstrenehm 13 tm 1-2 lb 1- lh d- 0.5 0.8 1.0 1.0 gia hyl dglliitligh lrl arz d a eitfziiiggf 0.4 0.4 Mlxture 11a 11b 11d examet y 0 eamine pen ame y P 1 t b d f bri ether 1.4 2.0 3.0 12.0

Into these mixtures were introduced completely un- Example 12 treated rayon cord (TD 1650/1 x 2) and the same rayon cord pretreated with the following impregnating mixture: Tests were cal'fled out Wlth Para-formaldehyde 111 a P b ht manner analogous to Example 2. Mixtures 12a to 12d b 1 0 arts y 2 0 were used which differed from those in Example 2 in Natural m bar atex 6 g"; 15 containing the following additives in addition to the con- Latex of a copolymer of uta lene, styrene an stituems of the basic mixture 1:

-v1nyl pyridine, 40% 62.5 Precondensed resorcinol formaldehyde resin 20.0 Additives to basic mixtumnn Formaldehyde solution, 30% 20.0 parts by weight Water 1872-5 Mixture 12a 12b 120 12d N t r dditi t-' t d: 2100-0 8 il /r 'i bi ackni fffi 2 5??? 35.0 35.0 10.0 10.0 Total dry content 6%. Silica tiller 1.. 30.0 30.0 The filaments were incorporated and vulcanised by the gjfgf g igy 3 f3 process descnbed 111 Example 8. The static bond strength was determined by a method analogous to that described in Example 8.

The dynamic bond strength, on the other hand, was determined by clamping the test strip described above into the movable part of a test machine and heating it to 80 C. The projecting ends of the cord filaments were fixed to the stationary part of the machine. The rubber was then moved to and fro 500 times per minute with a total stroke of 2.5 mm. (i125 mm.) The time required for the cord filament to become detached from the rubber under this stress was determined (in minutes).

The dynamic test method employed is recorded on pages 78 to 81 of Bayer-Mitteilungen fiir die Gummi- Industrie, N0. 29.

The test results obtained are shown in the following table:

The following bond strength were recorded:

Bond strength in kg. per 2.5 cm.

Mixture Nylon fabrlc.

Example 13 Static and dynamic bond strength at 80 C.

Mixture 10a Mixture 10b Mixture 10c Mixture 10d Stat. D yn. Stat. D yn. Stat. Dyn. Stat. Dyn. Tyre cord Org.) (mm.) (kg.) (mm.) (kg.) (min.) (kg.) (111111.)

Untreated Rayon cord 2.4 19 6.3 3.3 19 12. 0 216 Rayon cord impregnated with latex plus resorcinol formaldehyde resin 7. 5 184 9. 8 115 10. 0 211 12. 6 259 Example 11 The influence of the additive according to the invention on the bond strength between a conveyor belt fabric and the friction/cushion compound based on styrene-butadiene rubber was tested. The following mixtures were used:

Parts by weight Mixture 11a 11b 11c 11d Styrene butadiene rubber-. 100. 0 100. O 100. 0 100. 0

HAF black 20. 0 20. 0

Stearie acid 1. 5 1. 5 1. 5 1. 5

Phenyl-a-naphthyla ne 1. 5 1. 5 1. 5 1. 5

Zine oxide 5. 0 5. 0 5. 0 5. 0

BenZthiazyl-Z-cyclohexyl sulphenamide. 1. 25 1. 4. 1.6 1. 6

Thiuramie monosulphide 0.15 0. 15 0. 15 0. 25

Sulphur 1. 8 1. 8 1. 8 1. 8 Hexamethylol melamine pentamethyl ether 2. 5 2. 5

The tests were carried out in a manner analogous to Example 2, but a conveyor belt fabric of the following structure was employed.

The mixtures were prepared in an internal mixer at 150 C. without resorcinol and without formaldehyde splitter and without any special precautions. After cooling to about 90 C., 5 parts by weight of the above solution were added together with sulphur and vulcanisation accelerators.

Tests analogous to those in Example 1 carried out on the mixtures gave practically the same bond strengths as in Example 1.

In a further experiment, a solution of resorcinol in hexamethylolmelamine pentamethylether was subsequently added at 120 C. instead of at mixing temperature of 90 C. Here again the same bond strengths were obtained as previously whereas there was a distinct drop in bond strengths when a preliminary mixture of rubber and resorcinol was used in accordance with Example 1 and melamine ether was subsequently added at 120 C.

The process comprising the use of the resorcinol solution is thus not only easier to handle but also less sensitive to changes in temperature.

Example 14 In a manner analogous to Example 13 also in order on the mill 2.5 parts by weight of resorcinol were first Varied mixture components in dissolved in 4.2 parts by weight of xylene-formaldehyde parts by welght resln with heating. ThlS solution was added as in Ex- M t ample 13 at the end of the process of mixing the rubber x 18a 18b 18d mixture. Nature of 1titlamlponentsz The results of bond strength tests were the same as in Silica i; ':""""""""1;3939122:555-353-"55:5 Example 13 and thus showed that resorcinol solutions in g q u 2 6 2- 2 2 5 2. 2-2 2- 5; plasticisers may also be added to advantage. f Pentamethylolmelaminn 1. 0 1. 0

Example 15 Rayon cord (TD 1650/1 x 2), nylon cord (TD 1680/ 6 Tests were carried out whlch corresponded to those in 1 x 2) g F: cord (TD 1000/1 Dlolen Example 1 but in which 2.5 parts by weight of resorcinol f 16 of veffmlgten GlanzstofiFabnken/wupp*{tal were replaced by (a) 25 parts by weight of or Trevrra GPA of Farbwerke Hoechst), none of WhlCh phenol and (b) 44 Parts by Wight of resorcinol filaments had undergone any pretreatment, were then inacetate corporated by vulcamsatron and tested as described in Ex- Tests yielded practically the same results as in Example The following results are obtained: ample 1 except that for untreated rayon, the values for (b) were 20% higher Static bond strength (kg.) at 80 C.

20 Mixture 18a 18b 18c 18d 189 1st Example 15 Rayon cord, untreated 2.8 5.4 5.6 43 3.3 9.8 are 2t 22-; a? at 0 GS 61' 001 ,L'lll 1'83 8 nu. Mixtures 15a to 151 were prepared and tested in the y manner analogous to Example 2. Thread rupture- Additions to basic mixture I in parts by weight Mtxture 15a 15b 15c 150 159 151 15g 15h 151 Type of additives:

M'I black 35.0 35.0 10.0 35.0 10.0 35.0 10.0 35.0 10.0 Silica filler I. 30. 0 a0. 0 a0. 0 30. 0 Resorcinol 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Tetramethylol acetylene diurea 2.0 2.0 Hexamethylene tetr ne 2. 0 2. 0 Methylnnnaminnm-ntnnitriln 2. 0 2. 0 N,N-dimethylolurea. 2. 5 2. 5

The results were as follows:

Mixture 15a 15b 15c 15d 150 151 15g 15h 151 Rayon fabric" 1.5 3.5 11.5 2.4 9.5 4.9 13.3 2.7 9.9 Nylon fabric 1.1 5.4 17.5 1.9 7.3 3.2 9.4 2.7 6.9

Example 17 Example 19 The following mixtures 16a and 16d were prepared by The following mixtures were prepared on a mixing a method similar to that in Example 2: mill:

f basic mature 1 Constituents of mixture in 11 pa 5 by Welg t parts by Weight Mixture 16a 1 b 1 0 1 d Mhrmre 19a 19b 19c 19d Type of additives: Nature of constituen ts. gg g gfigfi 3&0 $83, Chlorobutadiene rubber 100.0 100.0 100.0 100.0 u m'l'infil 2.5 l

"'6'6"" 6 6 Hexamethylolmelaminepentagnesium 0x1 4. 0 4. 0 4. 0 4. 0 mthymh" 5 Z1ncoxide 5.0 5.0 5.0 5.0 %tebarltc 111mg 1. 5 1. 5 l. 5 1. 5 i u y es er Thick polyamlde wires (dlameter 21 mm on the glycome acid 5.0 M m 50 one hand and steel cord, both raw and coated with brass Xylene-formaldehydepes1n (structure: 7 x 3 x 0.15 mm.) on the other hand were g lfi sgrflaphthylaminan 3.2 2.2 3.2 3.2 incorporated and vulcanised into these mixtures in the nie-tel lg'tiiridiii'eilj -I 110 1:0 1:0 1:0 same way as the polyester and nylon cord filaments of Tetmmethyltthlllmmw o monosulpmde 1.0 1.0 1.0 1.0 Example 8 and tested at 80 C. Resoreinnl 2.5 2,5 Hexamethylplrlnelllamine 2 5 2 5 Bond strength at 80 0. Pen ame y at er Mixture 16a 16b 16c 16d 5 Thick polyamide wires- 2.1 2. 6 2. 2 19. 2 g evv stesg cor i g-g 1 3 -2 8-; When the rubber nuxture had cooled to about 90 C., ee e resorcinol and hexamethylolmelamine pentamethyl ether Exam 1e 18 were added in a manner analogous to Example 13 in the P form of a solution of resorcinol in the formaldehyde split- Mixtures based on butadiene-acrylonitrile rubber of the type described in Example 7 were used. All the components not mentioned in the following table were the same as in Example 7. Only the following substances were altered:

together in the zone of contact between the filaments and the rubber mixture.

What we claim is:

1. In the process of bonding a non-preimpregnated textile material or a metal directly to a rubber composition, the improvement which comprises incorporating in said rubber composition vulcanizing ingredients, a formaldehyde donor in an amount of 0.2 to 10% by weight based on the weight of the rubber in said composition, a member selected from the group consisting of resorcinol, m-aminophenol, m-phenylenediamine, resorcinol diacetate, resorcinol propionate, resorcinol butyrate, resorcinol monomethylether, resorcinol propylether and 1,5-dihydroxynaphthalene and finely dispersed silica filler in an amount of at least 15% by weight based on the weight of the rubber in said composition and having a surface area of 70-400 m. /g., bringing the non-preimpregnated textile material or metal in direct physical contact with resulting rubber composition and vulcanizing said resulting rubber composition.

2. The process of claim 1 wherein said rubber composition contains 15 to 70% by weight of said silica filler based on the weight of the rubber in said composition.

3. The process of claim 2 wherein said rubber composition contains from 20 to 60% by weight of said silica filler.

4. The process of claim 1 wherein the surface area of said silica is 80-200 m. g.

5. The process of claim 1 wherein the ratio by weight of said member selected from said group and said formaldehyde donor is between 02:1 and 2: 1.

6. The process of claim 1 wherein said formaldehyde donor is selected from the group consisting of hexamethylolmelamine pentamethylether, hexamethylolmelamine, tetramethylolhydrazone dicarbonamide, N allyl 1,3,5-dioxazine and N-phenyl-1,3,5- dioxazine.

7. The process of claim 1 wherein said rubber composition contains up to 5% by weight of stearic acid based 4 on the weight of rubber in said composition.

8. A material bonded directly to a vulcanized rubber composition, said material comprising a non-preimpregnated textile material or metal and said rubber composition containing, prior to vulcanization, vulcanizing ingredients, a formaldehyde donor in an amount of 0.2 to

10% by weight based on the weight of the rubber in said composition, a member selected from the group consisting of resorcinol, m-aminophenol, m-phenylenediamine, resorcinol diacetate, resorcinol propionate, resorcinol butyrate, resorcinol monomethylether, resorcinol propylether and l,S-dihydroxynaphthalene and finely dispersed silica filler in an amount of at least 15 by weight based on the weight of the rubber in said composition and having a surface area of -400 m. g.

9. The bonded material of claim 8 wherein said rubber composition contains 15 to 70% by weight of said silica filler based on the weight of the rubber in said composition.

10. The bonded material of claim 9 wherein the rubber in said composition contains from 20 to 60% by weight of said silica filler.

11. The bonded material of claim 8 wherein the surface area of said silica is -200 mF/g.

12. The bonded material of claim 8 wherein the ratio by weight of said member selected from said group and said formaldehyde donor is between 0.221 and 2:1.

13. The bonded material of claim 8 wherein said formaldehyde donor is selected from the group consisting of hexamethylolmelamine pentamethylether, hexamethylolmelamine, tetramethyolhydrazone dicarbonamide, N- allyl-1,3,5-dioxamine and N-phenyl-1,3,5-dioxazine.

References Cited UNITED STATES PATENTS 2,955,102 10/1960 Clayton et al. 260--79.5

3,366,583 1/1968 Wilson 260-3 3,411,970 11/1968 Perrin 161--227 X 3,018,207 l/ 1962 Danielson 161--110 M D 2,746,898 10/ 1953 Buckwalter et a1. 161241 FOREIGN PATENTS 1,078,320 3/ 1960 Germany.

0 ALFRED L. LEAVITT, Primary Examiner C. B. COSBY, Assistant Examiner US. Cl. X.'R. 

